The Collaborative International Dictionary of English v.0.48:
Offhand \Off"hand`\, a. Instant; unprepared; ready; extemporaneous; unrehearsed; as, an offhand speech; offhand excuses; an offhand comment. -- adv. In an offhand manner; as, he replied offhand. [1913 Webster]WordNet (r) 3.0 (2006):
off-hand adv 1: without preparation; "I don't know the figures off-hand" [syn: off-hand, ex tempore]